Serial Thyroid Profile Across the Third Trimester in Preeclampsia: A Case-Control Study from a South Indian Tertiary Centre

Abstract

Background: Preeclampsia complicates 5-15% of hospital deliveries in India and remains a leading cause of maternal mortality. Pregnancy alters thyroid economy, and small studies have linked thyroid dysfunction to preeclampsia, but the direction and consistency of this association across serial third-trimester visits in Indian tertiary settings has not been established. This study compared serum tri-iodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH), measured serially at three third-trimester visits, between women with preeclampsia and normotensive controls, and related the thyroid trend to concurrent blood-pressure trajectories.
Methods: This observational case-control study was conducted over 12 weeks in the Department of Obstetrics & Gynaecology, King George Hospital, Visakhapatnam. Of 220 pregnant women screened, 140 were excluded for pre-existing thyroid disease or other comorbidities. Twenty women with preeclampsia diagnosed after 20 weeks of gestation (Arm A) and 60 normotensive controls (Arm B) were followed. Serum T3, T4, TSH, and blood pressure were recorded at baseline (7th month) and at two subsequent visits (8th and 9th month). Values were compared within each arm across visits using two-way repeated-measures ANOVA and are reported descriptively between arms. Significance was set at p < 0.05.
Results: TSH was higher in Arm A than in Arm B at every visit (6.42 ± 0.43 vs 1.71 ± 1.20 μIU/mL at baseline; 5.34 ± 0.58 vs 1.84 ± 1.15 μIU/mL at visit 1; 4.89 ± 0.63 vs 1.92 ± 1.08 μIU/mL at visit 2). T3 and T4 were also higher in Arm A throughout, though the between-arm separation was narrower than for TSH. Arm A showed a significant within-arm shift in thyroid profile across visits (baseline vs visit 1, p = 0.004; visit 1 vs visit 2, p = 0.003; baseline vs visit 2, p = 0.002), while Arm B showed none (p = 0.896, 0.659, 0.632). Systolic and diastolic blood pressure fell significantly across visits in Arm A (p = 0.004 and p = 0.001) but not in Arm B (p = 0.286 and p = 0.172).
Conclusion: Serum TSH was consistently and significantly elevated throughout the third trimester in preeclampsia relative to normotensive pregnancy, with a trajectory that changed significantly across gestation in cases but not controls; T3 and T4 differences were of smaller magnitude. TSH warrants further evaluation as a low-cost adjunct in preeclampsia risk assessment, in adequately powered, multicentric, first-trimester cohorts that pair free-hormone assays with established angiogenic markers.